This invention relates to an antiglare film which, when disposed on the front of CRTs (cathode ray tubes) displays or liquid crystal displays, serves to diffuse light externally incident on these displays, thereby reducing glare.
In CRT displays, accelerated electrons collide with phosphors located on the inner side of the front glass to impart energy to the phosphors. This permits the phosphors to emit light, and, in general, red, green, and blue lights outgo on the front side. In liquid crystal displays, the liquid crystal per se does not emit light. Since, however, light is applied from the backside to enhance the visibility of liquid crystal images, on the whole of the display, light is emitted toward the front.
When the display is used in a room, light from lighting equipment, such as a fluorescent lamp, enters the surface of the display and is reflected from the display surface. This causes glaring of the display screen or reflection of a fluorescent lamp on the display screen, making it difficult to perceive letters and the like displayed on the screen.
The disposition of an antiglare film, having a light diffusing layer formed by coating a silica-containing resin coating composition onto a transparent substrate film, on the front of the display to diffuse external light causative of glare, and consequently to alleviate the glare of the display screen, has been already carried out in the art.
Conventional antiglare films include one wherein concaves and convexes have been formed on the surface of a light diffusing layer through the agglomeration of particles of agglomerative silica or the like, one wherein resin beads having a larger particle diameter than the thickness of the coating have been added to impart concaves and convexes on the surface of the coating, and one wherein an embossing film having concaves and convexes on its surface had been laminated onto the surface of an unsolidified coating to transfer the shape of concaves and convexes onto the surface of the coating followed by the separation of the embossing film.
All the above conventional antiglare films have light diffusing properties, a certain level of antiglare effect, and, in addition, by virtue of the thin film form, can be easily applied to displays.
However, when light emitted from the display toward the front is passed, through the antiglare film, shining called xe2x80x9cscintillationxe2x80x9d occurs on the film surface, disadvantageously posing a problem of deteriorated visibility of displayed images.
The following properties are important for an antiglare film which, in use, is disposed on the front of a display: (1) high level of anti-scintillation properties; (2) high image sharpness; (3) high light transmittance (=total light transmittance); and (4) high antiglare properties derived from light diffusing properties (=high level of capability of preventing the reflection of external light from a fluorescent lamp or the like external light reflection preventive properties)). None of the conventional antiglare films simultaneously satisfy all the above property requirements.
Accordingly, it is an object of the present invention to provide an antiglare film simultaneously satisfy all of the property requirements, that is, (1) high anti-scintillation properties, (2) high sharpness of transmitted images, (3) high total light transmittance, and (4) high external light reflection preventive properties without significantly altering the form of the conventional antiglare film, that is, the thin film form, and a process for producing the same.
The present inventors have found that, in the formation of an antiglare film by coating of a resin coating composition with particles dispersed therein, the formation of good concaves and convexes and the provision of an antiglare film satisfying various properties required of light diffusing films can be realized by a method which comprises the steps of: selecting a resin and non-agglomerative particles having a specific article diameter so that the difference in refractive index between the resin and the particles is 0.05 to 0.15; bringing the resin and the non-agglomerative particles to a coating composition using, as a solvent, a good solvent for the resin and a poor solvent for the resin; coating the coating composition onto a substrate film to form a coating; and drying the coating, whereby, in the course of the drying, as the amount of the good solvent contained in the coating decreases, the poor solvent acts to cause the gelation of the particles and the resin.
According to one aspect of the present invention, there is provided an antiglare film comprising at least a light diffusing resin layer formed of non-agglomerative light-transparent fine particles dispersed in a light-transparent resin, the light-transparent fine particles having a particle diameter of 1.0 to 5.0 xcexcm, the difference in optical refractive index between the light-transparent fine particles and the light-transparent resin being 0.05 to 0.15, the content of the light-transparent fine particles being 5 to 30 parts by weight based on 100 parts by weight of the light-transparent resin, the surface roughness of the light diffusing resin layer being 0.12 to 0.30 in terms of center line average roughness (Ra) and 1.0 to 2.9 in terms of ten-point average roughness (Rz).
In another embodiment of the antiglare film according to the present invention, the light diffusing resin layer is stacked on a transparent substrate.
According to the present invention, the thickness of the light diffusing resin layer is preferably 1 to 3 times the diameter of the light-transparent fine particles.
According to the present invention, the antiglare film preferably has an image sharpness of 80 to 300 and a level of external light reflection preventive properties of 5 to 70.
According to another preferred embodiment of the present invention, the light-transparent resin is a cured product of an ionizing radiation-curable resin.
According to another aspect of the present invention, there is provided a process for producing an antiglare film, comprising the steps of:
providing a coating composition comprising non-agglomerative light-transparent fine particles, a light-transparent resin, a good solvent for the light-transparent resin, and a poor solvent for the light-transparent resin, the light-transparent fine particles having a particle diameter of 1.0 to 5.0 xcexcm, the difference in optical refractive index between the light-transparent fine particles and the light-transparent resin being 0.05 to 0.15, said ingredients being contained in the coating composition in an amount of 5 to 30 parts by weight for the light-transparent fine particles based on 100 parts by weight of the light-transparent resin and in an amount of 20 to 1,000 parts by weight for the solvent in terms of the total amount of the good solvent and the poor solvent, the parts by weight ratio of the good solvent to the poor solvent being 100:20 to 100:70;
coating the coating composition onto a substrate; and
then drying the coating to reduce the weight ratio of the good solvent to the light-transparent resin, whereby, while allowing the light-transparent fine particles and the light-transparent resin to gel, the coating is solidified to create concaves and convexes on the surface of the coating.
According to a preferred embodiment of the present invention, the light-transparent resin and the good and poor solvents are selected from the following combinations:
(a) a combination of an acrylate resin, a good solvent for the acrylate resin selected from the group consisting of toluene, methyl ethyl ketone, ethyl acetate, n-butyl acetate, and cyclohexanone, and a poor solvent for the acrylate resin selected from the group consisting of methanol, ethanol, n-butanol, and isopropanol;
(b) a combination of a cellulosic resin, a good solvent for the cellulosic resin selected from the group consisting of ethyl acetate, n-butyl acetate, acetone, and cyclohexanone, and a poor solvent for the cellulosic resin selected from the group consisting of methanol, ethanol, n-butanol, and isopropanol;
(c) a combination of an epoxy resin, a good solvent for the epoxy resin selected from the group consisting of methanol/toluene (xe2x80x9c/xe2x80x9d referring to mixing), ethanol/xylene, methyl ethyl ketone, ethyl acetate, n-butyl acetate, and methyl isobutyl ketone, and a poor solvent for the epoxy resin selected from the group consisting of toluene, xylene, cyclohexanone, and cyclopentane;
(d) a combination of a urea melamine resin, a good solvent for the urea melamine resin selected from the group consisting of ethyl acetate, n-butyl acetate, n-butanol, and n-hexyl alcohol, and a poor solvent for the urea melamine resin selected from the group consisting of toluene and xylene; and
(e) a combination of a urethane resin, a good solvent for the urethane resin selected from the group consisting of ethyl acetate, n-butyl acetate, and methyl ethyl ketone, and a poor solvent for the urethane resin selected from the group consisting of methanol and ethanol.
In the above process, the drying is preferably carried out at a temperature of 20 to 100xc2x0 C.
According to another embodiment of the process, the light-transparent resin is an ionizing radiation-curable resin and, after the formation of concaves and convexes on the surface of the coating, an ionizing radiation is applied to the coating to cure the coating through crosslinking.